Group

Group (of species) [ Taxonomy ]	Dictionary of botanic terminology - index of names
Synonyms: Complex, Aggregate (of species)

A species is referred as a "group" (also complex or aggregate) when several different subspecies, variety and forms often with subtle variation in morphology are described from across its vast range.

The variability in such a “complex” may be due to polymorphisms among different populations and individuals of the same species which are ecologically or geographically separated and whose members exhibit high, but not complete, specificity. Otherwise a complex may be due to the presence of multiple distinct (but morphologically similar) species living together in the same habitat.

The classification of a "complex" species remains problematic. There are in fact two tendency about how to classify species : by their differences or by their similarities depending on personal approach of taxonomists to recognizing differences or commonalities between organisms (See also: Lumpers & splitters)

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Holdfast roots [ Botany ]
Dictionary of botanic terminology - index of names

Some species of climbing plants develop holdfast roots which help to support the vines on trees, walls, and rocks. By forcing their way into minute pores and crevices, they hold the plant firmly in place.

Climbing plants, like the poison ivy (Toxicodendron radicans), Boston ivy (Parthenocissus tricuspidata), and trumpet creeper (Campsis radicans), develop holdfast roots which help to support the vines on trees, walls, and rocks. By forcing their way into minute pores and crevices, they hold the plant firmly in place. Usually the Holdfast roots die at the end of the first season, but in some species they are perennial. In the tropics some of the large climbing plants have hold-fast roots by which they attach themselves, and long, cord-like roots that extend downward through the air and may lengthen and branch for several years until they strike the soil and become absorbent roots.

Major references and further lectures:
1) E. N. Transeau “General Botany” Discovery Publishing House, 1994